Vergence Sensitivity in 5-10 Week-Old Infants
25.11, Saturday, 16-May, 5:15 pm - 6:45 pm, Talk Room 1
Eric Seemiller1, T. Candy1; 1Indiana University School of Optometry
Introduction Fine motor alignment of the two eyes is necessary for appropriate binocular experience, yet in adults it appears that binocular processes are responsible for fine motor alignment. There is substantial evidence that infants start to respond to binocular retinal disparity (a primary cue for motor alignment) at 3-5 months of age. However, rudimentary eye alignment is possible from birth and matures with age. How does eye alignment develop in the absence of adult-like binocular processes? Here we investigate the sensitivity of vergence eye movements in 5-10 week old humans to a target moving in depth, while addressing the possible influence of accommodation. Methods Infants (5-10 weeks) and adult controls viewed a naturalistic movie stimulus on a screen that moved sinusoidally in depth at three different amplitudes (1.0, 0.5 and 0.25 MA) at 0.1 Hz. A photorefractor measured horizontal eye position and refractive status at 25 Hz. FFTs provided the amplitude spectra of both vergence and accommodation responses for comparison with the stimulus spectrum. Signal plus noise : noise ratios (SNRs) were calculated by dividing the response at the stimulus frequency by the mean of the adjacent frequencies. Results Vergence SNRs were significantly different from 1 (signal + noise equals noise) at even the smallest amplitudes tested (mean SNR = 2.10; p =0.03). suggesting that infants of 5-10 weeks could generate a vergence response to a full cue stimulus moving in depth at 0.25 MA (~30 minutes of disparity) Accommodation responses were only significant for the two larger amplitudes (mean SNRs = 2.84, 1.47; p = 0.04, 0.03). Adult SNRs were all significant for accommodation and vergence (p < 0.002). Discussion Infants make vergence responses to 0.25 MA stimulus movements at least one month prior to the documented onset of disparity sensitivity. Implications for development of eye alignment will be discussed.